ACAP - Global Gravity Field Modelling from Orbit Data based on the Acceleration Approach

A number of satellite missions dedicated for recovering the Earths gravity field have been launched in the past: CHAMP (2000), GRACE (2002), and GOCE (2009). By these missions homogeneously and globally distributed gravity field related observations and precise satellite positions are available. There are various approaches to determine gravity field models from precise orbit data. The Institute of Theoretical Geodesy and Satellite Geodesy has already implemented the energy balance approach in the frame of previous projects and is successfully applying the software for GOCE and CHAMP gravity field modeling. The acceleration approach is based on Newtons second law of motion which states that orbit-derived accelerations of a satellite are directly related to the gradients of the gravitational potential. While the acceleration approach benefits from the full exploitation of the 3D orbit information of every epoch, the energy balance approach computes only one pseudo-observation from the 3D position. Therefore the acceleration approach achieves a higher redundancy which results in a better estimation of geopotential coefficients. The key issue of the acceleration approach is the use of a suitable numerical differentiation scheme. The Taylor-MacLaurin method is already in use in the energy balance approach and has been proved to be a powerful tool in terms of numerical differentiation and attenuation of high frequencies at the same time. The final gravity field models based on GOCE and CHAMP data will be compared and validated.